The present invention provides a device which optically senses the presence and movement of an object in contact with an optically transmissive platen and generates a control signal indicative thereof. According to a specific embodiment of the invention, the control signal is for controlling the movement of a pointer or cursor on a display. According to another specific embodiment, the control signal is for controlling various functions of an apparatus such as, for example, volume and channel selection on a television.
There are currently a number of different technologies on the market for moving a pointer on a computer display screen, the most common being a "mouse". The mouse employs a rubber ball in frictional contact with a flat surface. The rotation of the rubber ball caused by movement of the mouse across the surface is translated into movement of the pointer on the screen. Typically, the rotation of the ball is sensed using two wheels in contact with the ball, each of which tracks rotation of the ball in one dimension. The wheels generate electrical signals which are, in turn, combined to generate a composite signal for controlling movement of the pointer on the screen in the two dimensions. Selection of symbols or icons on the screen indicated by the pointer is effected by actuation of a switch on the mouse. Another type of mouse operates similarly to the typical mouse except that the rotation of the ball is tracked by optical sensors.
One alternative to the mouse is the Glidepoint pad manufactured by Alps Electronics. The Glidepoint is a touch sensitive pad which comprises a matrix of pressure sensitive switches across which the user moves a fingertip or other object such as, for example, a pencil. The matrix of switches tracks the movement of the fingertip across the surface of the pad and generates a two-dimensional control signal which controls the movement of the pointer. As with the mouse, a switch is provided for selection of items on the screen. Alternatively, selection may be effected by rapid, intermittent actuation of any portion of the switch matrix, i.e., tapping on the Glidepoint pad.
Another alternative to the mouse is the TrackPoint pointing stick provided by IBM with its Thinkpad line of laptop computers. The Trackpoint is essentially a miniature joystick which protrudes from the center of the laptop's keyboard. To move the pointer up and down, the user pushes the stick forward and backward. To move the pointer left and right, the user pushes the stick left and right. The Trackpoint senses the forces exerted against it, translating these forces into electrical signals corresponding to the directions in which the stick is pushed. These electrical signals are then used to control the movement of the pointer on the display.
In the field of television remote controls, control signals for volume control and channel selection are typically generated using mechanical switches. The control signals are then transmitted to the television using infrared energy. One type of remote control employs four mechanical momentary switches arranged in a diamond configuration with the left/right switches controlling channel selection and the up/down switches controlling the volume. Another type of remote control employs a four-position rocker switch (e.g., circular or cross-shaped) with similar functionality associated with the four positions.
The above-described pointing and remote control devices each have associated advantages for particular applications. However, all of them share the same disadvantage in that each includes components which require mechanical actuation to effect movement of the display pointer. Because of inherent reliability problems associated with mechanical components, pointing and control devices having no mechanical components are therefore desirable.